1. Field of the Invention
This invention relates to exterior curtain wall system utilizing multiple framed panels. Each individual framed panel consists of a facing panel supported by four perimeter members. In this type of curtain wall system, there are two typical field formed wall joints, namely, horizontal wall joint and vertical wall joint. These field formed wall joints are the potential sources of water leakage problem. The wall joint designs of this invention eliminate the dependency of sealant line integrity for watertight performance. In addition, this invention allows thermal movement of the facing panel to be unrestrained by the perimeter frame and vice versal. Also this invention allows easy replacement of each individual facing panel. The facing panel material can be glass panel, natural or artificial stone panel, composite honeycomb panel, composite foam panel, or metal plate.
2. Description of the Prior Art
The mechanism of water leakage phenominon can best be described in the following manner. The first step is that the exterior rain water running along the exterior wall surface reaches the sealant lines of the field formed wall joints. The second step is that if the sealant lines are not perfect (i.e. pin holes or small cracks in the sealant lines), the water reached the sealant lines will infiltrate through the pin holes or cracks in the sealant lines under a positive pressure between the exterior air and the interior air. The positive pressure always exists on the windward wall due to the wind forces and is sometimes magnified by the suction type air exchange system of the building. The prior art systems for solving the water leakage problem can be classified into the following four generations.
The first generation of the wall joint design is to seal off the wall joints right along the exterior wall surface using field applied caulking. The facing panel is structurally supported by an interior wall frame system using curable silicone caulking as the structural connection. This type of design is an attempt of making a perfect seal in the field (i.e. no pin hole or hairline crack in the sealant line is allowed). This perfect seal concept requires careful field executions of the following items.
(1) The caulking backer (known as backer rod) must be placed in the proper location to give an adequate and uniform caulking depth.
(2) The caulking bonding surfaces must be free of water, oil, or dirt before the application of caulking (i.e. no erection on a rainy day).
(3) The caulking must be tooled after the application.
It can be easily seen from the above that this perfect seal concept is highly dependent of the field workmanship. In addition, cyclic thermal movements of the facing panel surface induce stress reversals within the sealant causing latent sealant failure due to stress fatigue. Aside from the sealing reliability and durability problems, the caulked wall joints are known to have two aesthetic problems, namely, streaking due to chemical release and dirt collection due to electrical charge. Another drawback of the system is the need of temporary support before the curing of the structural caulking and the associated removal of the temporary support and the patching of the sealant due to the removal of the temporary support.
The second generation of the wall joint design utilized the concept of controlled water leakage. The first design feature is to use interior perimeter aluminum extrusion members structurally connected to and sealed to the facing panel in the shop to form interlocking tongue-and-groove horizontal and vertical panel side joints. The tongue-and-groove joints are hidden behind but close to the facing panel and are sealed with nonbonding gasket material to allow free thermal movements of the panel surface without causing sealant stresses. However, the nonbonding contacting surface of the gasket represents a continuous hairline crack which will allow water infiltration through the sealant line under positive differential pressure, therefore, it requires a second design feature to control the water leaked through the gasket line. The second design feature is to create a horizontal gutter (known as internal gutter) behind the gasket line within the depth of the perimeter aluminum extrusion to collect the water leaked through the gasket line and to provide drainage holes from the bottom of the internal gutter to the exterior horizontal panel joint such that the water collected within the internal gutter can be drained to the outside after the positive pressure differential has been subsided. In addition, it is required to splice and to seal the horizontal internal gutter across the vertical wall joint, to seal off the holes at four corner intersections, and to seal between the horizontal and vertical gasket lines (known as marriage seal) in the field to complete the system. Again, these three field sealing operations must rely on careful workmanship in the field. In addition, these field applied sealants are subjected to stresses due to thermal movements of the wall panel surface. Another drawback of the design is that the exposed drainage holes will allow the water to infiltrate freely into the internal gutter under positive pressure, therefore, substantial water buildup in the internal gutter is expected even in there is no water leakage in the gasket line. This high water buildup in the internal gutter necessitates a high gutter leg design and increases the risk of water leakage at the gutter splice joint. Another drawback of the design is that the potential leakage source of the gutter splice is hidden behind the plate, thus, repair can only be done from the interior side which usually involves costly interior restoration. Additional aesthetic problem is the water stain on the panel surface below the drainage holes.
The third generation of the wall joint design is that the facing panel is structurally sandwiched between an exterior flange and an interior flange of the perimeter aluminum extrusion and sealed in between. To reduce the probability of water leakage, three different design methods have been used in the industry. The first design method is to completely seal the gap between the exterior flange and the facing panel using silicone caulking. This method has the drawbacks of the first generation design except the need of temporary support. The second design method is to use gasket with pressure applied by the force of screw known as "pressure bar system" to seal the gap between the exterior flange and the facing panel. However, the nonbonding contacting surface of the gasket represents a continuous hairline crack which will allow water infiltration through the sealant line under positive differential pressure, therefore, it requires to use the seating surface of the facing panel to act as an internal gutter with exposed outward drainage holes. In this arrangement, water may overflow the gutter and seep through the interior sealant line under high pressure differential. The third design method is to create an internal horizontal gutter and down spout drainage system in combination with the first or the second method. The third method has a higher rate of success in preventing water leakage. However, it costs much more. In addition, the required thermal expansion joints of the exposed aluminum members are difficult to arrange and to maintain sealing integrity.
The fourth generation design which is my prior invention (U.S. Pat. No. 4,840,004) utilizes interior perimeter frame to support the facing panel and to create a water drainage system within a pressure equalized wall cavity eliminating the dependency of field workmanship for water tight performance. However, due to the interior frame arrangement, differential thermal movement between the facing panel and the interior frame creates stresses within the shop applied sealant line which may result in shop applied sealant line failure leading to water leakage problem. Therefore, even though this design represents a major improvement of eliminating the dependency of field workmanship for watertight performance, it still has to depend on the long term integrity of the shop applied sealant line. In addition, due to the structural connection between the facing panel and the interior frame, replacing an individual damaged facing panel is extremely difficult.
In summary, all the prior art design methods must rely on long term sealing integrity of the field and/or shop applied sealant line. It is obvious that consistent perfect field or shop applied sealant line is practically unachievable. Therefore, the probability of water leakage problem continues to exist.